Turn on of sky-blue thermally activated delayed fluorescence and circularly polarized luminescence (CPL) via increased torsion by a bulky carbazolophane donor

Nidhi Sharma; Eduard Spuling; Cornelia M. Mattern; Wenbo Li; Olaf Fuhr; Youichi Tsuchiya; Chihaya Adachi; Stefan Bräse; Ifor D. W. Samuel; Eli Zysman-Colman

doi:10.1039/C9SC01821B

Turn on of sky-blue thermally activated delayed fluorescence and circularly polarized luminescence (CPL) via increased torsion by a bulky carbazolophane donor†

Nidhi Sharma,‡^ab Eduard Spuling,

‡^c Cornelia M. Mattern,^c Wenbo Li,^b Olaf Fuhr,

^d Youichi Tsuchiya,

^ef Chihaya Adachi,

^efgh Stefan Bräse,

*^ci Ifor D. W. Samuel

*^b and Eli Zysman-Colman

*^a

Author affiliations

* Corresponding authors

^a Organic Semiconductor Centre, EaStCHEM School of Chemistry, University of St Andrews, St Andrews, Fife, KY16 9ST, UK
E-mail: eli.zysman-colman@st-andrews.ac.uk

^b Organic Semiconductor Centre, SUPA, School of Physics and Astronomy, University of St Andrews, North Haugh, St Andrews, UK
E-mail: idws@st-andrews.ac.uk

^c Institute of Organic Chemistry (IOC), Karlsruhe Institute of Technology (KIT), Fritz-Haber-Weg 6, 76131 Karlsruhe, Germany
E-mail: braese@kit.edu

^d Institute of Nanotechnology (INT) and Karlsruhe Nano-Micro Facility (KNMF), Karlsruhe Institute of Technology, Hermann-von-Helmholtz-Platz 1, D-76344 Eggenstein-Leopoldshafen, Germany

^e Center for Organic Photonics and Electronics Research (OPERA), Kyushu University, 744 Motooka, Nishi-ku, Fukuoka 819-0395, Japan

^f JST, ERATO, Adachi Molecular Exciton Engineering Project, Kyushu University, 744 Motooka, Nishi-ku, Fukuoka 819-0395, Japan

^g Department of Chemistry and Biochemistry, Kyushu University, 744 Motooka, Nishi-ku, Fukuoka 819-0395, Japan

^h International Institute for Carbon Neutral Energy Research (WPI-I2CNER), Kyushu University, 744 Motooka, Nishi-ku, Fukuoka 819-0395, Japan

ⁱ Institute of Toxicology and Genetics (ITG), Karlsruhe Institute of Technology (KIT), Hermann-von-Helmholtz-Platz 1, D-76344 Eggenstein-Leopoldshafen, Germany

Abstract

The carbazolophane (Czp) donor unit (indolo[2.2]paracyclophane) is introduced to the design pool of donors in thermally activated delayed fluorescence emitters. The increased steric bulk of the annelated donor unit forces an increased torsion between the carbazole and the aryl bridge resulting in a decreased ΔE_ST and an enhancement of the thermally activated delayed fluorescence in the triazine-containing emitter CzpPhTrz. Further, the closely stacked carbazole and benzene units of the paracyclophane show through-space π–π interactions, effectively increasing the spatial occupation for the HOMO orbital. The chiroptical properties of enantiomers of [2.2]paracyclophane reveal mirror image circular dichroism (CD) and circularly polarized luminescence (CPL) with g_lum of 1.3 × 10⁻³. rac-CzpPhTrz is a sky-blue emitter with λ_PL of 480 nm, a very small ΔE_ST of 0.16 eV and high Φ_PL of 70% in 10 wt% doped DPEPO films. Sky blue-emitting OLEDs were fabricated with this new TADF emitter showing a high maximum EQE of 17% with CIE coordinates of (0.17, 0.25). A moderate EQE roll-off was also observed with an EQE of 12% at a display relevant luminance of 100 cd m⁻². Our results show that the Czp donor contributes to both a decreased ΔE_ST and an increased photoluminescence quantum yield, both advantageous in the molecular design of TADF emitters.

This article is part of the themed collections: Most popular 2019-2020 materials and energy chemistry articles and Most popular 2018-2019 materials chemistry articles

Chemical Science

Turn on of sky-blue thermally activated delayed fluorescence and circularly polarized luminescence (CPL) via increased torsion by a bulky carbazolophane donor†

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Turn on of sky-blue thermally activated delayed fluorescence and circularly polarized luminescence (CPL) via increased torsion by a bulky carbazolophane donor

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